1. Field of the Invention
The present invention relates to an angular velocity sensor.
2. Description of the Related Art
Japanese Patent No. 3,606,164 (corresponding to U.S. Pat. No. 6,473,290, referred to as the patent document 1 hereafter) discloses an angular velocity sensor that includes a substrate, a movable unit coupled with the substrate through a supporting beam, a comb-shaped movable electrode provided in the movable unit, and a comb-shaped fixed electrode provided in the substrate. The movable unit is movable in a detecting direction due to the supporting beam. The comb-shaped fixed electrode includes a plurality of fixed electrode units arranged in the second direction at predetermined intervals. The comb-shaped movable part includes a plurality of movable electrode units. The movable electrode units are engaged with the fixed electrode unit in such a manner that one of the movable electrode units is arranged between adjacent two of the fixed electrode units. The angular velocity sensor detects angular velocity by detecting a change in capacitance of a capacitor provided by the fixed electrode units and the movable electrode units when the movable unit is displaced in the second direction due to Coriolis force along the second direction.
Japanese Patent No. 3,512,004 (referred to as the patent document 2 hereafter) discloses an angular velocity sensor that includes a substrate, a vibrator coupled with the substrate through a beam and a frame, a servo electrode, and a servo control circuit. The vibrator is movable in a first direction and a second direction that are parallel to a surface of the substrate and are perpendicular to each other. The servo electrode and the servo control circuit restrict vibration of the vibrator in the second direction. The angular velocity sensor calculates a servo voltage applied to the servo electrode based on the vibration of the vibrator in the second direction and calculates the angular velocity based on the servo voltage.
Each of the above-described angular velocity sensors is manufactured by processing a silicon-on-insulator (SOI) substrate by a known micromachine technique. In such processing, machining error occurs in some measure. When machining error occurs, the vibration in the first direction may escape in the second direction, and an escaped component may reduce a detection accuracy of angular velocity. The angular velocity sensor disclosed in the patent document 1 does not have a configuration for restricting influence of the escaped component. Thus, the detection accuracy of angular velocity may be reduced by the escaped component.
In the angular velocity sensor disclosed in the patent document 2, the servo electrode and the servo control circuit restrict vibration of the vibrator in the second direction. Thus, influence of the escaped component can be reduced.
However, in the angular velocity sensor disclosed in the patent document 2, if machining error occurs in interval and width of electrodes, a servo voltage change with respect to an angular velocity change may be reduced in the servo electrode and the servo control circuit. As a result, the detection accuracy of angular velocity may be reduced.